[R-sig-Geo] as() and conversion from character to factor

[MacQueen, Don]

I just noticed that in the following sequence the final step to
SpatialGridDataFrame converts the character column to factor, whereas the
previous ones do not. Source the following little script, and it will
hopefully show what I'm seeing. Shouldn't this be consistent?

Thanks
-Don


require(sp)
require(maptools)

tstdf <- expand.grid(x=1:3, y=1:3)
tstdf$ch <- rep('a',nrow(tstdf))

tstsp <- tstdf
coordinates(tstsp) <- c('x','y')
proj4string(tstsp) <- CRS('+init=epsg:32610')

tstpx <- as(tstsp, "SpatialPixelsDataFrame")

tstgrd <- as(tstpx, "SpatialGridDataFrame")

print(class(tstdf$ch))
print(class(tstsp$ch))
print(class(tstpx$ch))
print(class(tstgrd$ch))


#########
I get:

> print(class(tstdf$ch))
[1] "character"
> print(class(tstsp$ch))
[1] "character"
> print(class(tstpx$ch))
[1] "character"
> print(class(tstgrd$ch))
[1] "factor"
#########







> sessionInfo()
R version 2.15.1 (2012-06-22)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] C

attached base packages:
[1] stats     utils     datasets  grDevices graphics  methods   base

other attached packages:
[1] maptools_0.8-16 lattice_0.20-6  foreign_0.8-50  sp_1.0-0

loaded via a namespace (and not attached):
[1] grid_2.15.1 rmacq_1.1-8








-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062